Pluggable power cell for an inverter

ABSTRACT

In one embodiment, a power cell chamber for a drive system includes moveable and fixed portions. The moveable portion includes a rectifier stage to rectify an input signal received from a secondary winding of a transformer to provide a rectified signal and an inverter stage having a plurality of switching devices to receive a DC signal and output an AC signal. This moveable portion can be slidably adapted within a cabinet of the drive system. In turn, the fixed portion includes a DC link having at least one capacitor to receive the rectified signal and provide the DC signal to the inverter stage.

BACKGROUND

Generally, equipment referred to as a power converter, inverter or driveis used to provide power to another piece of equipment such as a motor.Specifically, such a converter (converter is used generally herein torefer to converters, inverters and drives) is coupled to a utilityconnection to receive incoming input power such as three-phase AC power.The converter conditions the power to provide a conditioned power to theequipment or load. In this way, incoming power to the load may be ofimproved efficiency, leading to reduced costs to operate the equipment.

Multi-level power converters have been gaining popularity mainly due toimproved input and output harmonics content, better electromagneticcompatibility, and higher voltage capability. These improvements inpower conversion are achieved by using a multiple voltage step strategy.One common multi-level inverter topology is based on H-bridge inverters,in which multiple H-bridge inverters are connected in series. Since thistopology consists of series power conversion cells, the voltage andpower level may be easily scaled.

Multi-level power converters are used to provide power to a load such asa motor. Oftentimes, such multi-level converters are implemented as alarge piece of equipment that is housed in a cabinet that receivesincoming power, e.g., from a utility connection, conditions the powerand provides it to a coupled load. In general, a drive system includesone or more transformers that have secondary windings that are coupledto individual power cells that perform rectification, inversion, andother conditioning tasks. Typically, to perform these functions eachpower cell includes a rectifier, DC link capacitor and inverter, amongother such equipment, and each such power cell is packaged together intoa module.

However, as voltage and power requirements increase in a system, thesemodules can be relatively cumbersome, bulky and expensive. For example,in medium voltage (MV) applications, such power cells can easily exceed50 pounds due to the size of the DC link capacitors and other componentspresent. Another drawback of this conventional design of power cells ofa drive system includes a costly and complex customized isolation systemas voltage levels increase from a few kilovolts to tens of kilovolts. Ingeneral, power cells are provided as a fixed enclosed module customizedfor a given power and voltage level. For example, power cells for 4160Vat 1000 HP applications will radically increase foot print and weightover a power cell designed for 3300V at the same output power. Inaddition, the overall MV converter package must be individually designedto meet a particular power output, such as 5000 HP, 10000 HP, 20000 HPapplications, control, and protection specifications.

In current medium voltage drives, a cascaded topology is implementedusing a partial modular design. Specifically, the only subcomponent ofthe system that is common across drive products of a family is the powercell, which as described above contains the power components includinginverter, rectifier, and DC-link. Current medium voltage drives haveexcluded all other system components, including transformers, control,cooling system, communication distribution, packaging, and electricalinsulation, from a modular approach. Instead, these major components areoptimized for voltage and power rating of a specific design and thus arenot easily transferable to other drive ratings.

SUMMARY OF THE INVENTION

Embodiments introduce a cell integration method to reduce cell footprint and weight, and a method to increase the cell power density. Inaddition, embodiments provide a cell voltage isolation method to meetrequirements up to several tens of kilovolts and provide a modular highpower building block or cabinet configuration. This high power buildingblock provides an efficient way to series and/or parallel power cells.The number of series or parallel power cells is only limited by thedrive application. The cabinet configuration is based on a modular powertransformer, small size pluggable power cell system, a reconfigurableelectrical insulation method, and a master-slave control scheme.Embodiments provide overall system power and voltage scalability,standardized design, and easy reconfiguration to meet a wide power rangein MW levels.

In various embodiments, a complete modular design establishessubcomponents for most major drive elements including power cell,transformer, control, cooling system, communication distribution,packaging, and electrical insulation. Each component may have differentversions to accommodate multiple voltage and power ratings.

According to one aspect of the present invention, a power cell chamberfor a drive system includes moveable and fixed portions. The moveableportion includes a rectifier stage to rectify an input signal receivedfrom a secondary winding of a transformer to provide a rectified signaland an inverter stage having a plurality of switching devices to receivea DC signal and output an AC signal. This moveable portion can beslidably adapted within a cabinet of the drive system. In turn, thefixed portion includes a DC link having at least one capacitor toreceive the rectified signal and provide the DC signal to the inverterstage. The fixed portion is affixed in the cabinet, and the moveableportion is separate from the fixed portion.

In some implementations, the fixed portion includes an input cellprotection mechanism coupled between a corresponding secondary windingand a power service bus, and a bypass block to enable bypass of thepower cell chamber. The moveable portion can be formed of an enclosurehaving switching devices of the inverter stage on a first side and aplurality of rectification devices of the rectifier stage on an oppositeside. In addition, a low inductance path can be coupled between theswitching devices and the rectification devices, and may include atleast one local capacitor to snub transients.

Yet another aspect of the present invention is directed to local lowinductance bus capacitors coupled to a rectifier and inverter. Suchcapacitors may be of a removable portion of a power cell chamber. Inturn, a power capacitor of the power cell chamber, which may be of afixed portion of the power cell chamber, can provide a DC bus voltage tothe removable portion. The local capacitors can be useable in adiagnostic mode in which the power capacitor is not available, and canfurther provide snubbing protection in a normal operation mode of asystem including the power cell chamber.

A still further aspect of the present invention is directed to a mediumvoltage drive system with modular cabinets, each of which includes atransformer bay to house at least one transformer and a power cell bayincluding cell chambers each having a protective enclosure in which tohouse a power cell. Each modular cabinet may further include a cabinetcontroller bay having a cabinet controller to receive reference controlsignals from a master controller. In turn, the master controller iscoupled to the cabinet controllers to receive input current information,output current information, command parameters regarding a selectedoperating point of the medium voltage drive system, and statusinformation from the modular cabinets, and to provide the referencecontrol signals to the cabinet controllers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram view of a drive system adapted in a cabinet inaccordance with one embodiment of the present invention.

FIG. 2A is a schematic diagram of components within a power cell chamberin accordance with one embodiment of the present invention.

FIG. 2B is a block diagram illustrating connections available in a powerservice bus in accordance with an embodiment of the present invention.

FIG. 2C is another view of a power service bus in accordance with oneembodiment of the present invention.

FIG. 3 is a block diagram view of a power cell module in accordance withone embodiment of the present invention.

FIG. 4 is a breakaway diagram of a chamber of a power cell cabinet inaccordance with one embodiment of the present invention.

FIG. 5 is an illustration of an example embodiment of a winding geometryof a modular transformer in accordance with one embodiment of thepresent invention.

FIG. 6 is a block diagram of a system in accordance with an embodimentof the present invention.

FIG. 7A is an illustration of a cabinet in accordance with oneembodiment of the present invention.

FIG. 7B is a side view of the cabinet that illustrates air flow forcooling in accordance with an embodiment of the present invention.

FIG. 8A is a block diagram of a modular system configuration inaccordance with one embodiment of the present invention.

FIG. 8B is a block diagram of a parallel modular system configuration inaccordance with an embodiment of the present invention.

FIG. 8C is a block diagram of a series modular system configuration inaccordance with one embodiment of the present invention.

FIG. 9A is a flow diagram for a basic control loop for a mastercontroller in accordance with one embodiment of the present invention.

FIG. 9B is a flow diagram for a basic control loop for a cabinet inaccordance with one embodiment of the present invention.

FIG. 9C is a flow diagram for a method for performing control of a powercell in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

In various embodiments, a power cell chamber can be separated intomultiple portions, namely a stationary or fixed portion and a moveableportion. These different portions may be joined by a power service bus.In this way, a module or other housing or enclosure that forms themoveable portion can be made to be relatively small and lightweight ascompared to a conventional power cell. This allows for greater ease ofcustomer access and removal, repair and replacement operations on thesemoveable portions of a power cell. In turn, the moveable portion may beplugged into a power service bus that couples the moveable portion withthe fixed portion within the power cell chamber. The fixed portion ofthe chamber may include various components that would conventionally bepresent in a single power cell enclosure including, for example, a DClink by way of one or more capacitors. As such components can berelatively reliable over a number of years, these components present inthe fixed portion may be provided on an opposite side of the powerservice bus from the moveable portion. As used herein, “fixed” or“stationary” means that a component is physically attached directlywithin a cabinet, not readily customer accessible, and cannot beinserted and removed by simple pluggable/slidable means. Instead,special access and tools are needed to insert or remove the component.In contrast, “moveable” or “pluggable” means a component or group ofcomponents that are easily inserted and removed from a cabinet, e.g.,via sliding, plugging and so forth without the need for tools, andhaving ready customer access.

Embodiments may provide for a modular cabinet-based drive system thatcan be used to provide regulated power at a wide range of voltages. Forexample, some applications may be used for low voltage applications. Asused herein, low voltage is used to denote voltages of 600 volts andbelow. Others may be used for medium voltage applications. As usedherein, medium voltage is used to denote voltages between approximately600 volts and 35000 volts. Still further, owing to the separationbetween components of a conventional power cell and isolation affordedwithin a cabinet (as discussed below), embodiments also may be readilyused for high voltage (HV) applications. As used herein, high voltagemeans greater than 35000 volts, e.g., 69000 volts.

Referring now to FIG. 1, shown is a block diagram view of a power cellcabinet in accordance with one embodiment of the present invention. Asshown in FIG. 1, cabinet 10 may house at least a portion of a drivesystem such as a medium voltage drive system that can be a multi-levelinverter. The view of FIG. 1 is with respect to a front portion of thecabinet. In general, the cabinet is arranged such that a plurality oftransformers 22 _(a)-22 _(c) are present in a transformer bay 20, whichmay be configured in a lower portion of cabinet 10. In turn, a pluralityof power cells 32 _(a)-32 _(i) may be configured within a power cell bay30 of cabinet 10. In the embodiment shown in FIG. 1, nine such powercells are present, although the scope of the present invention is notlimited in this regard. Also, while shown as single modules in the viewof FIG. 1, understand that the portions of the power cells shown in FIG.1 may correspond to the moveable portions adapted within enclosures.Unseen in FIG. 1 are the fixed portions of the power cell modules, whichmay be adapted to a rear portion of a power service bus, also not shownin FIG. 1.

In some implementations, a single modular power cell cabinet may besufficient to provide desired power levels for a given system. In suchimplementations, a cabinet controller 45 present in a controller bay 40may be used to handle control of the drive system. However, manyembodiments may aggregate a plurality of power cell cabinets with arespective cabinet controller 45 along with a single master controllercabinet 40 to control the cabinet arrangement and increase the powercapabilities. In these implementations, controller bay 40 including cellcontroller 45 may in turn be coupled, e.g., via a fiber optic interfaceto a master controller cabinet (not shown in FIG. 1). Furthermore, inimplementations in which a single power cell cabinet is present, aseparate cabinet may provide a user interface. That is, to provide useraccess to information regarding a drive system, a user interface may bepresent. Such user interface may include a display and an inputmechanism such as a key pad or keyboard to enable user input ofinformation and control of various operations including diagnostics andso forth. In other implementations, a master controller cabinet mayinclude such a user interface.

With reference to the transformers of FIG. 1, each transformer may beconfigured in a horizontal manner having a core 24 and multiple windingsadapted there around, including a primary winding and a set of secondarywindings. In addition, some embodiments may further include one or moreauxiliary windings to provide power to auxiliary equipment such as fansor the like. Each transformer 22 may be a three-phase transformer thatreceives three-phase power from a utility connection and provides powerto one or more of the power cells (although only a single phase is shownin FIG. 1). More specifically, each transformer may include three setsof secondary windings to provide power to a corresponding power cell. Inone implementation transformer 22 a may provide power to the power cellswith which it is generally vertically aligned with, namely power cells32 a, 32 d, and 32 g. Similar connections can be configured fortransformers 22 b and 22 c. However, other implementations are possible.Note that the primary windings, secondary windings or both may bephase-shifted in some implementations.

By providing transformers in a generally horizontal configuration,improved airflow is realized. For purposes of cooling the transformersand the cabinet in general, a substantially linear and laminar airflowmay be provided, e.g., from forward to rear of the cabinet such that theair blows through the windings of the transformers. While ambient aircooling can be used in many implementations, some embodiments mayprovide some type of liquid cooling for the transformers as well.Further details regarding the horizontal nature of the transformers willbe discussed below.

As further seen in FIG. 1, each power cell chamber 33 (i.e., both themoveable and fixed portions) can be configured as an enclosure (only onerepresentative such chamber shown in FIG. 1). Such cell chamber can beformed using an insulative material such as a polypropylene or otherplastic or other such material. Still further, to provide electricalisolation between the power cells and other equipment in cabinet 10, anisolation barrier 34 can be provided in each chamber (note only one suchisolation barrier 34 is shown). As seen, isolation barrier 34 is formedof a plurality of individual members in an interlocking manner toprovide efficient isolation. In various embodiments, isolation barrier34 may be formed of sheets of an insulating material such as FORMEX™ orother such material. While shown with only a few such members for easeof illustration in the embodiment of FIG. 1, understand that many suchmembers, e.g., 2 or many more may be provided, as these individualmembers can be of relatively thin width, e.g., 9.8 to 125.2 mils. Inthis way, an insulating bubble is formed around each power cell tofacilitate voltage insulation. Such insulation may enable a singlegeneric cabinet architecture to be used with a wide variety of voltages,from low voltage applications all the way up to high voltageapplications. Generally as the voltage application increases, the numberof sheets and thus relative thickness may also increase.

Understand that while shown with this particular implementation in theembodiment of FIG. 1 with the power cells configured above transformers,the scope of the present invention is not limited in this manner.Furthermore, understand that additional components may be present in agiven drive system, and the illustration of FIG. 1 is at a high level toidentify the main components and their general location within a system.

Referring now to FIG. 2A, shown is a schematic diagram of componentswithin a power cell chamber in accordance with one embodiment of thepresent invention. As shown in FIG. 2A, chamber 100 is adapted toinclude both the fixed and moveable portions. A given drive system mayinclude multiple such chambers to form the drive system. In variousimplementations a power cell module 110 may correspond to the moveableportion of the power cell chamber and may be accessed via a front panelof a cabinet, whereas a fixed portion 115 of the chamber may beaccessible via a rear panel of the cabinet or via a front panel when thecell module 110 is not present or is otherwise removed. Thus as shown inFIG. 2A, from right to left generally corresponds to a direction from afront to a rear of a cabinet. Details of the movable power cell aredescribed further below. In general, the moveable portion may includethe rectification and inverter stages of a cell (but not the DC-linkpower capacitor).

Power cell module 110 may couple to a power service bus 120 via aplurality of pluggable terminals located on a back portion thereof.Power service bus 120 may have various connectors to mate with theterminals of power cell module 110. In some embodiments, power cellmodule 110 may be installed via blind mating connections withcorresponding connectors of power service bus 120. As will be describedbelow, power cell module 110 may include a rectifier section and aninverter section. The rectifier section may include a plurality ofdiodes coupled to the inputs from the transformer secondary, along withat least one parallel-connected local capacitor that in turn is coupledto a local capacitor low inductance bus. Similarly, the inverter sectionmay be, for example, an H-bridge inverter including a plurality ofswitching devices such as IGBTs and further may include aparallel-connected local capacitor. The local capacitor may providediagnostics and snubber protection capability to the power cell. Indifferent implementations, this capacitor may be sized from a few tensto a few hundreds of nanofarads. In turn, the inverter section is alsocoupled to the local capacitor low inductance bus. This bus may beconstructed in a manner to provide a low inductance path. In variousembodiments, the inductance may be between a few nanohenries to lessthan 20 nanohenries and the bus may be formed from a laminate materialand provide connections between these two sections in a low inductancemanner.

In a given implementation, power cell module 110 may be formed havingdual cooling plate heat sinks, e.g., on top and bottom. In variousimplementations, various controller boards may be present in module 110.One of the boards provides gate signals to control the H-bridgeinverter, while a second board provides input current and DC bus voltagesensing capability for the power cell. A third board may be incommunication with these controller boards and may be also implementedwithin the plug-in section of the cell chamber 110 and which in turn canbe coupled via a fiber optic interface to the respective cabinetcontroller. A power supply also may be present within module 110, andwhich may be used to provide a low voltage supply to, e.g., the internalcell controller boards.

In the embodiment shown in FIG. 2A, input, output, DC bus, and controlsignal connections of a power cell may be provided via a number of blindmating connectors to couple to bus 120. Note that bus 120 may alsoinclude a DC low inductance bus. In general, this bus may use at leastsome of the following to enable a low inductance connection: the bus maybe formed of a laminate material, e.g., multiple copper sheets and aninsulation sheet to provide electrical isolation to the arrangement. Asseen in FIG. 2A, the AC output of the power cell is connected usingplug-in connectors 125 ₁ and 125 ₂. In turn, an input connection to thecell from secondary windings of a transformer may be coupled to powercell 110 via connectors 126 ₁-126 ₃ (in a three-phase implementation).In turn, a DC bus connector 128 may couple a DC bus link between powercell 110 and a capacitor 130. In one embodiment, connector 128 may beformed of a single connection having a plurality of concentric fixedconnectors to mate with concentric fixed terminals to connect to a lowinductance DC bus. The concentric connector 128 may connect to a cellDC-link power capacitor 130 and which is implemented in a fixed portion115 of the power cell chamber formed on the opposite side of powerservice bus 120. The capacitor thus may be a remote capacitor withrespect to the moveable power cell. In one such implementation thisconcentric connector may be a type of coaxial cylindrical cable thatreduces the DC bus inductance. In other embodiments, low inductance maybe realized by providing a number of connections for the positive andnegative portions of the DC bus, e.g., four connectors in parallel,arranged horizontally or in any other pattern, two each for positive andnegative portions. Note also a control connector 129 may provide variousstatus and control signals through power service bus 120.

In one embodiment, capacitor 130 may be a single film power capacitor ora plurality of single film capacitors connected in series or parallel ora combination to fit a specific cell design. The capacitor configurationmay range from thousands of microfarads to tens of thousands ofmicrofarads and from a few tens to a few hundreds of amperes rms. Thecapacitor configuration 130 may operate from a DC bus which may be ratedfrom a few hundred volts to several thousands of volts. Otherimplementations may use electrolytic or other type of capacitors. Eachindividual capacitor may further be associated with a dischargeresistor. More than one such capacitor may be present, and thus the term“capacitor” as used herein refers to a combination of one or morecapacitors. Capacitor configuration 130 may also be located on top orbottom of the moveable section of the power cell chamber but within thecell chamber.

In addition, fixed portion 115 may further include an input cellprotection mechanism 140 such as circuit breakers or other protectionmechanisms e.g., fuses to couple between the secondary windings of atransformer and power service bus 120. The input cell mechanismprotection 140 may provide reliable short circuit protection andoverload protection within a few 60 Hz current cycles. The control tripscheme to operate mechanism 140 (not shown) may be implemented inmoveable portion 110. Not shown in the embodiment of FIG. 2A are variouscontrol and switching signals that may couple between a cell and amaster or cabinet controller (which may be outside of a given power cellchamber, but present in another part of a cabinet, for example).

In addition, a cell bypass block 150 may be provided in fixed portion115, which may provide redundancy power/bypass to a given power cell ina cell failure mode. This mechanism may be implemented using a shunttrip contactor controlled from a cabinet controller via the plug-insection and service bus. For example, during operation when a powerswitch failure is detected by signals sent to a master controller, themaster controller may act to actuate block 150 to thus create a shortcircuit between the outputs of a power cell having a failure. Withreference to FIG. 2A, by actuating a coil within bypass block 150, ashort circuit between terminals P1 and P2 can be realized to thus bypassthis power cell in case of a malfunction. For example, if power cell 32g (of FIG. 1) is disabled due to a failure in phase A, power cells 32 dand 32 a may be also disabled in phases B and C via the mastercontroller to allow the drive system to continue functioning at reducedpower and balance voltage output.

In one embodiment, block 150 may be an electronic switch coupled via alatching relay to a cabinet controller (not shown). The latching relaythus acts to take the signals from the cabinet controller andautomatically control switching of bypass block 150 to open and close tothus provide bypass by responding to a fault command or other adversecondition. Similar connections may be present between a correspondinglatching relay and input cell protection mechanism 140 to cause thebreaker or other protection mechanism to be enabled to thus preventinput power from being applied to a given power cell. For instance, if afailure occurs in the rectifier section and detected by a current sensorlocated in the cell input (not shown in FIG. 2A), the input protectionmechanism 140 may disable the power to the cell via 140, followed by theactuation of bypass block 150 to isolate the troubled cell. Under thisscenario, a master controller may act to disable the entire drive systemor bypass this cell to continue operation at reduced power. In someimplementations the connection between the cabinet controller andlatching relay or shunt trip circuit may be via fiber optic, althoughthe scope of the present invention is not limited in this regard.

The structure of power service bus 120 holds concentric DC bus and otherterminal mating accesses (plug-in style). Power service bus 120 mayintegrate bus bars for cell series output, bus bar for cell input, a lowinductance laminated DC bus to connect to the DC-link powercapacitor(s), and a G-10™ material to provide structural support andinsulation between electric buses. In this way, series coupling of agroup of power cells can occur to provide a phase output line to a loadcoupled to the drive system. In different implementations, the servicebus can be formed using a division wall (e.g., G-10™ material) or anopen structure to provide for air circulation.

Referring now to FIG. 2B, shown is a 3-D mechanical model illustratingconnections available in a power service bus in accordance with anembodiment of the present invention. As shown in FIG. 2B, power servicebus 120 may be formed using insulation material, e.g., G-10 and includescontacts for cell input, output, DC link, and control signals (notshown). Specifically as seen in FIG. 2B, at a top portion of powerservice bus 120, the cell outputs P1 and P2 may be adapted. Furthermore,the three connections L1-L3 at a bottom of the power service bus mayprovide the inputs from secondary windings of a transformer, while theDC link connections 128 may be provided via four individual connections,two positive and two negative.

Referring now to FIG. 2C, shown is another view of the power service busthat shows part of a moveable portion of a power cell chamber thatprovides connections to the cell inputs, outputs, as well as the DC linklaminated buses in the moveable portion. Note that on the top portion ofmoveable module 110, a plurality of switching devices 114, which may beIGBTs are seen, while rectification devices 117 are present at thebottom of the cell. Switching devices 114 may be coupled between alaminated DC bus 119 and bus bars 118. As also seen in FIG. 2C, theoutput from a power cell is routed via connectors P1 and P2 from busbars 118. Connectors P1 and P2 may provide connection to another powercell with which power cell 110 is coupled in series, namely anotherpower cell of the same phase output line.

While shown with this particular implementation in the embodiment ofFIGS. 2A-C, the scope of the present invention is not limited in thisregard. For example, while it is assumed in this embodiment that powercell moveable portion 110 may not include the components of fixedportion 115 described above, in some implementations, a limited amountof local capacitance available in the power cell may be combined withthe fixed capacitance present in the fixed portion within the power cellchamber in accordance with an embodiment of the present invention.

Referring now to FIG. 3, shown is a block diagram view of a power cellmodule in accordance with one embodiment of the present invention. Asshown in FIG. 3, module 160 may be a basic representation of a removableportion of a power cell. Not shown, an enclosure may be present andwhich may have various components present therein including, for examplea local controller, input current and heat sink sensors, power switchgate drivers and a modular HV power supply. In addition, module 165includes a split heat sink formed of cooling plate members 162 _(a) and162 _(b), present on opposite sides of housing 165 to provide forimproved thermal control and increased power density for module 160.While not shown in FIG. 3 for clarity, understand that the heat sinkmembers may have a comb, fin, or fan-like structure to efficientlydissipate heat. The heat sink structure may include a cooling plate witha cooling fluid circulating in pipes through the plate with input/outputleaving on the same or opposite sides of the housing. Differentcomponents can be coupled to the two heat sinks. In the implementationshown in FIG. 3 on a top portion, switching devices of an inverter stagemay be present. As an example, switching devices 164 _(a) and 164 _(b)may be IGBTs. While shown in this front view in FIG. 3 as including onlytwo such IGBT dual modules, understand that in various implementationsan H-bridge of a power cell may include six-pack IGBT modules, and allof which may be adapted on a top portion of power cell enclosure 165. Onthe bottom portion, rectification devices 166 _(a)-166 _(c) of arectifier stage may be present. Again, while shown with three suchdevices in FIG. 3, understand that additional rectification devices maybe present in different embodiments. In some embodiments, therectification section may be replaced by an active front end having sixIGBT modules to provide regeneration capability in addition to therectification. Also, by adapting the major components of the moveableportion of the power cell around an exterior of an enclosure 165, easeof access to the components for heat dissipation as well as increase ofpower density by maintaining same foot print for a wide range of powerand utilizing none or limited DC-link capacitance. This also has adramatic impact on size and weight reduction, and how diagnostics andremoval, repair and replacement operations are realized.

To provide a low inductance path between the rectifier and invertersections, two local film capacitors 168 that provide local ripple andfull DC-link current circulation, may be adapted to the outside ofenclosure and coupled to the switching devices and rectification devicesby way of corresponding sets of terminals (note the terminals are notshown in FIG. 3). This low inductance path has reduced parasitics andprovides an adequate path for DC current circulation, as well as forperforming snubbing of transients that may arise during normal operationto improve inverter cell performance. In this way, local capacitors 168may be used to provide a low inductance path directly between rectifierand inverter to enable smoothing of a noisy signal during normaloperation, and diagnostics/testing capabilities for a single cell. Thatis, in contrast to the one or more capacitors provided in a fixedportion of a power cell chamber which are used to provide the bulkcapacitance needed to operate the inverter, the local capacitor(s) canact as snubbing circuitry to filter out unwanted voltage transientspresent at the inverter terminals. This is particularly so duringswitching events occurring in switching devices of the inverter. Whileshown with this simplified view in the embodiment of FIG. 3, understandthe scope of the present invention is not limited in this regard.

Referring now to FIG. 4, shown is a breakaway diagram of a cell chamberof a cabinet in accordance with one embodiment of the present invention.As seen in FIG. 4, chamber 33 includes a power cell insulator portion 32including rail members 35 at its bottom to allow a movable power cell tobe slidably mated into and removed from the chamber. Specifically, rails31 may enable corresponding rails 35 of the movable power cell to slide.As seen, multiple layers of an isolation barrier 34 may be present toprovide insulation to a power cell chamber. In this way, isolationbarrier 34 acts as a bubble or cocoon shell in which the power cellchamber is isolated from other equipment of a drive system. The numberof layers may depend on a rated voltage of the drive system. Forexample, depending on the thickness of the individual layers (which canrange from less than 1 mm to over 20 mm), operation isolation can exceed150 kV. In some implementations, 5 or more layers may be provided toenhance isolation.

In various implementations, the layers of isolation barrier 34 may bepresent between a perimeter of a chamber and rails 35 of the chamber. Asfurther shown in FIG. 4, additional insulation members 37 may be adaptedaround the power cell insulator portion 32 to enable improved insulationof the power cell. Note that the length of the layers of isolationbarrier 34 may extend beyond the length of the power cell module adaptedwithin chamber 33 to improve isolation. Furthermore, this extendedlength enables a single modular design to be used with power cells ofvarying rated voltage applications to enable a single modular design tobe used with drive systems having widely different voltage ratedcapabilities.

As described above, a cabinet may include a transformer bay, in whichone or more transformers are adapted. Such transformers may have a mainprimary winding, which may be a three-phase medium voltage winding thatreceives medium voltage power feed, e.g., from a utility connection. Inturn, a set of secondary windings each of which may be a three-phasesecondary winding may provide normal operating power to the power cells.These secondary windings may be phase shifted, e.g., by 20 degrees fromits neighboring secondary winding, however the scope of the presentinvention is not limited in this regard. In addition to the mainwindings for powering the power cells during normal operation, atransformer may further include auxiliary windings to enablepre-charging as well as to handle auxiliary functions, such as fordiagnostics, voltage sensing, fan power and so forth.

By separating a transformer into modular units, there is more surfacearea for the core and thus it can dissipate heat more effectively.Further, each modular core volume may reduce in size since the windingwindow may only need to accommodate one or a small number of secondarywindings per output phase. The modular approach allows a single unittransformer to be used across a wide voltage and power range. Byincreasing the number of modular units, a drive system in accordancewith an embodiment of the present invention can be capable of highervoltage and power with lower harmonic distortion.

In one embodiment of a drive system having multiple modulartransformers, the amount of phase shift of secondary and primarywindings can be calculated according to the following equations:

$\begin{matrix}{N_{S} = \frac{N_{dc}}{N_{T}}} & \lbrack {{EQ}.\mspace{14mu} 1} \rbrack \\{\alpha_{\sec} = \frac{360}{{2 \cdot N_{ph}}N_{s}}} & \lbrack {{EQ}.\mspace{14mu} 2} \rbrack \\{\alpha_{prim} = \frac{\alpha_{\sec}}{N_{T}}} & \lbrack {{EQ}.\mspace{14mu} 3} \rbrack\end{matrix}$where N_(T) is the number of transformer modules; N_(dc) is the numberof isolated DC sources; N_(S) is an integer number of the number ofsecondary windings in each transformer; N_(ph) is the number of phasesof a supply; α_(sec) is the secondary windings phase shift in eachmodule; and α_(prim) is the primary winding phase shift in each module.

Modular transformers may be manufactured using transformer manufacturingtechniques and implementing various types of winding designs for bothprimary and secondary windings. Primary windings may include bothextended delta configurations and a standard delta configuration.However, the connection of primary and secondary windings can be freelychosen. In various implementations, a desired phase shift may berealized by changing the geometry of the winding, e.g., by adjusting thenumber of turns of one or more coils of the transformer or taps withregard to other coils. By controlling the number of turns of coils andconnection method of them, a given phase shift can be realized.Secondary windings can include standard delta configurations, as well aspolygon configurations, where again by changing the size and/or turns ofone or more coils, different phase shifts can be obtained. Of course,other configurations or connections can be used to realize a desiredphase shift in different implementations.

As described above, modular transformers may be adapted horizontally toaid in cooling the transfer. FIG. 5 is an illustration of an exampleembodiment of a winding geometry of a modular transformer. As shown inFIG. 5 is a geometric illustration of a modular transformer 200. Asseen, transformer 200 may be a single modular transformer having agenerally horizontal configuration (i.e., the windings are wrappedaround a horizontal axis X) with a core 205, which may be an iron corehaving the different windings, both main and auxiliary, wrapped aroundhorizontal columns of the core. Generally, the windings may include aprimary coil 210 and a plurality of secondary windings 220. In addition,some implementations may further provide auxiliary power by way of a LVprimary auxiliary winding 230 and a LV secondary auxiliary winding 240.However, in some implementations, the auxiliary windings may not bepresent. Further, the scope of invention is not limited to only ahorizontal configuration as this method can be applied to a conventionalvertical configuration too.

While FIG. 5 shows a three-phase configuration, and thus having threecolumns for supporting windings, each adapted on a horizontal axis,reference herein will be with regard to a single phase. As shown, aspatial separation exists between the main coils and the primary LVauxiliary coil. This configuration causes a loose coupling with otherwindings and a high leakage inductance for the LV primary auxiliarywindings. However, the scope of invention is not limited in this aspectand other methods can be applied to generate high leakage inductancesfor the primary LV auxiliary winding. While the scope of the presentinvention is not limited in this regard, in a medium voltageimplementation in which core 205 is approximately 2 to 10 feet high,this separation may be on the order of between approximately 0.5 and 6inches to provide the desired high leakage inductance between theprimary auxiliary winding 230 and the main secondary windings 220 andmain primary winding 210.

As seen, the configuration of the main secondary windings 220 is suchthat these windings are wrapped concentrically around each other, andfurther that these windings are also concentrically wrapped around theauxiliary secondary winding 240. Note that in the implementation of FIG.5, auxiliary secondary winding 240 may extend substantially along theentirety of the column length of core 205 and may have the mainsecondary windings 220 wrapped there around.

Thus in the particular implementation, the secondary windings 220 may benext concentrically adapted, e.g., in order of a first phase-shiftedsecondary winding 220 a, a second phase-shifted secondary winding 220 c,and finally a non-phase shifted secondary winding 220 b. Finally,wrapped concentrically around these windings is the main primarywinding, MV winding 210. The spacing between coils corresponds tocooling method and isolation and voltage level of the coils. Thus whiledescribed above as a forced air cooling technique, this method can beapplied to natural cooled, and water cooled transformers. Varioustransformer manufacturing techniques can be used in realizing the coilsand insulation. As examples, different wire types (e.g., round, square,or so forth) and different insulation materials (e.g., NOMEX™ felt orpaper insulation, fiber, wood, epoxy, or so forth) can be used.

The configuration shown in FIG. 5 thus provides for loose couplingbetween the primary auxiliary winding 230 and the main windings 210 and220 (in particular, main secondary windings 220). However, differentwinding geometries or methods can be implemented to provide high leakageinductance for the LV auxiliary primary winding.

Note that in FIG. 5, direction from left to right may correspond from afront to a rear of a cabinet in which the transformer is adapted. Inthis way, a horizontal arrangement is realized such that air flow comingfrom an input mechanism such as a grill at a front panel of thetransformer bay may receive air which is pulled through the grill andacross the windings (and core) from a front to a rear portion of thecabinet. Then the air may be forced up through a rear of a cabinet andoutput via fans or other cooling members that act to pull the air acrossthe transformers and up and out through these exhaust fans. In this way,improved cooling can be realized as a large volume of air that travelsin a substantially linear and generally laminar flow can occur, withoutthe need for baffles or other air handling or director equipment. Notethat FIG. 5 shows only a single modular transformer and in variousimplementations three or more such transformers may be present in atransformer bay of a cabinet in accordance with an embodiment of thepresent invention. When multiple such transformers are present, spacingmay be maintained between the transformers such that at least someamount of open space is present between the windings of the twotransformers, such that air flow may pass and magnetic and electricisolation is maintained between the transformers.

When using auxiliary windings in accordance with an embodiment of thepresent invention at power-up of a drive, power is supplied through thehigh leakage inductance LV auxiliary primary winding(s). The highinductance of this set of windings can slow the rate of capacitorcharging and limit the in-rush current to the drive. Furthermore,another auxiliary secondary winding can be embedded into a transformermodule for providing power to cooling fans or any other auxiliary powerusage. Of course, a given system may not implement any auxiliarywindings.

Referring now to FIG. 6, shown is a block diagram of a system inaccordance with an embodiment of the present invention. As shown in FIG.6, system 600 may be a medium-voltage drive. Specifically, in theembodiment of FIG. 6, a three-phase, medium-voltage drive is shown thatincludes a plurality of power cell chambers 620 _(A1)-620 _(C3)(referred to in FIG. 6 as diode front end (DFE) cells). As seen, a localcell controller 626 _(A1)-626 _(C3) is associated with each of the powercell chambers. Understand that while shown as a single enclosure, eachof the power cell chambers may be separated into a fixed portion and amoveable portion and that the local cell controller may in someembodiments be adapted within an enclosure of the moveable power cell.Also, understand that while not shown in FIG. 6 for ease of illustrationa plurality of power service buses may be configured between thesedifferent portions of the power cells and furthermore may provide forconnections between each power cell and a master controller 640.

As seen, each of these local controllers may communicate with a fiberoptic interface 660. In some implementations, a pair of unidirectionalfiber optic channels may be coupled between each local controller andfiber optic interface 660. In turn, fiber optic interface 660communicates with a master controller 640 that further includes an ADC645.

Master controller 640 may provide control signals to fiber opticinterface 660 for transmission to the different local controllers. Inone embodiment, these control signals may be voltage reference signals,which cause the local controllers to perform certain processing togenerate the needed switching signals. In other implementations, theswitching signals themselves may be sent by master controller 640 fortransmission to the local cell controllers.

As further seen in FIG. 6, a signal conditioning board 650 may bepresent to sense or perform signal processing with regard to variousinformation, namely voltage and/or current information obtained bothfrom the input power source and the output of the different phase outputlines coupled to a load 630 which in one embodiment may be a motor, aswell as from an auxiliary secondary winding in accordance with anembodiment of the present invention.

In addition to the control information described above, additionalinformation from master controller 640 can be provided to the individuallocal controllers. In addition, the local controllers can provideinformation such as status information, both as to normal operation aswell as faults, over-temperature situations or so forth, back to mastercontroller 640. Master controller 640 may further be associated with auser input device 655 such as a keyboard and/or touch screen display andwhich may be adapted within a user interface bay to enable user input tocontrol various features such as speed, torque, selection of differentpower cells to be enabled and so forth, as well as to provide statusinformation to the user via a given display or other output means.

As shown in FIG. 6, input power to transformer modules 610 may includeboth a medium voltage source, e.g., from an input power supply such as autility connection, and a low voltage power source, e.g., from anauxiliary low voltage power source, as discussed above. Such sources maybe provided to a customer cabinet 605, which may be at a separatelocation from a cabinet of drive system 600. Cabinet 605 may include acontrol circuit to switch between powering of the drive by either themain power source or the auxiliary power source. For example, atpower-up, a switch 606, which may be a circuit breaker, of the lowvoltage auxiliary power line is closed such that power is provided totransformer module 610 through a normally closed contact 607 to enablepre-charging of the capacitors of the different power cells 620 via thislow voltage source. Accordingly, the capacitors of power cells 620 arecharged through LV auxiliary primary winding(s) of transformer module610 to a predetermined voltage level. Then after passing of apredetermined time, which may be on the order of approximately 50 to10000 milliseconds (ms), a main power supply power switch 608 (e.g., aMV circuit breaker) is closed. Normally closed contact 607 can be usedto disconnect the LV auxiliary power. By closing the main power supply,the capacitors are thus charged to their rated voltage. A timer orprogrammable logic controller (PLC) or other type of control circuit canbe used to control the process and sequence of switching. In anotherembodiment, the master controller can determine this charging time bymonitoring the DC-bus voltage of one or more power cells. After thecapacitors of power cells are charged to a predetermined level, themaster controller can send an activation signal to MV circuit breaker608. However in either implementation method, the sequence of switchingfor powering-up the drive is first to close the LV auxiliary switch 606(i.e. circuit breaker). After a predetermined time or receiving acommand from a controller, the LV switch 608 is opened and main powerswitch 608 (i.e., MV circuit breaker) is closed. Note in otherimplementations, direct connection form utility to drive system 600 mayoccur (i.e., without customer cabinet 605).

Referring now to FIG. 7A, shown is an illustration of a cabinet inaccordance with one embodiment of the present invention. As shown asFIG. 7A, a cabinet that houses a drive system, e.g., a medium voltagedrive system, includes a transformer bay 20, a power cell bay 30, a fanbay 40, and a cabinet controller bay 50.

The illustration of FIG. 7A further shows the horizontal configurationof three transformers 200 _(a)-200 _(c), each of which includes a corehaving three columns, one for each of three phases, each having ahorizontally aligned axis around which primary and secondary coils maybe concentrically wrapped. Also seen are the illustrations of individualpower cell chambers 32 _(a), which show the moveable portions that areformed of an enclosure with heat sinks adapted on top and bottomportions.

Referring now to FIG. 7B, shown is a side view of the cabinet thatillustrates air flow for cooling in accordance with an embodiment of thepresent invention. As seen in FIG. 7B, a grill or other input mechanism25 may be provided at a forward panel of transformer bay 20 to enableincoming air flow. As seen, the incoming air flow passes horizontallythrough transformers 200, as well as passing vertically up to the powercell bay. The laminar air flow through transformers 200 may then bevertically removed through an air duct at a rear of the cabinet by fanswithin fan bay 40.

FIG. 7B further shows the configuration of the power cell chambers whichare formed from the moveable enclosure 110, power service bus 120 andcapacitor of the fixed portion 115 (note that other components may bepresent in the fixed portion as discussed above, e.g., with reference toFIG. 2A). As seen in FIG. 7B, the air flow through the power cell baymay further be provided vertically upward via fans within fan bay 40.While shown with this particular implementation in the embodiment ofFIGS. 7A and 7B, the scope of the present invention is not limited inthis regard.

As described above, a modular power control system includes buildingblocks that can be used to configure systems having one or morecabinets. A modular system may include one or more cabinets, each ofwhich may be configured such as described above with regard to FIG. 1.Still further, a master control cabinet per system may be provided toenable centralized control for the overall system. Thus in variousembodiments, a power control system may include a master control cabinetand one more or more cell cabinets that can be identically configured.The number and interconnect configuration of the cell cabinets determinethe current and voltage capacity of the overall system. In differentimplementations, the cabinets can be configured in parallel for greatercurrent and/or in series for greater voltage applications.

The control and diagnostics for the modular system can also bedistributed among the major components. The master controller providescontrol information to each cell cabinet. Each cell cabinet provideslocal control of the power cells, via a cabinet controller. Statusinformation is provided from the power cells to each cabinet controller.The cabinet controller then provides cabinet status back to the mastercontroller. In various embodiments, diagnostics are run locally for eachmajor component. Each power cell controller, cell controller, and mastercontroller initiates local operations to assess operational readiness.Cell cabinet operational readiness is then communicated back to themaster controller, and the master controller then determines the overallreadiness of the system.

Referring now to FIG. 8A, shown is a block diagram of a modular systemconfiguration in accordance with one embodiment of the presentinvention. As shown in FIG. 8A, system 400 may be a minimal modularsystem, e.g., for a relatively low medium voltage application in whichonly a single power cell cabinet 420 is present and which in turn iscoupled to a load 430. As seen, cabinet 420 is coupled to receive inputpower from, e.g., a set of AC mains. Feedback information, namely theinput current and voltage may be provided via a feedback path 405 to amaster control cabinet 410, which may further receive a feedbackregarding the output voltage and current from power cell cabinet 420.

In other implementations, a different configuration may be realized.Referring now to FIG. 8B, shown is a block diagram of a parallel modularsystem configuration in accordance with an embodiment of the presentinvention. As shown in FIG. 8B, system 400′ includes a plurality ofpower cell cabinets 420 _(a)-420 _(n) coupled in parallel to increasedrive output current capability. Each power cell cabinet is paralleledto the AC mains and provides output current to load 430. The mastercontrol 410 maintains load sharing among cabinets 420 _(a)-420 _(n) byprocessing current feedbacks via 405 and 425.

In yet other implementations a series configuration is possible.Referring now to FIG. 8C, shown is a block diagram of a seriesconfiguration. As seen in FIG. 8C, system 400″ includes a plurality ofpower cell cabinets 420 _(a)-420 _(n) coupled in series, such that theoutputs are cascaded to provide a wide range output voltage capabilityto load 430. Similar feedback connections to master cabinet control 410are provided to preserve load voltage sharing among the power cellcabinets. Other implementations may use combinations of parallel andserial configurations to increase load voltage and current capability.

Referring to FIG. 9A, shown is a flow diagram of a basic control loopfor a master controller in accordance with one embodiment of the presentinvention. As shown in FIG. 9A, method 500 may be performed on acontinual basis by the master controller. Specifically, based on inputcurrent and output voltage and current information received in themaster controller, and various command parameters, including current andvoltage ratings, speed, frequency, torque and so forth, a voltagereference may be computed (block 510). In one embodiment, the voltage orcurrent reference may be computed using a standard motor vector controlalgorithm, e.g., processing torque and flux commands, and rotorposition. Next, it may be determined based on various information comingfrom the different cabinets whether the system is operating within itsoperating parameters (diamond 520). If not, an alarm may be triggered(block 525) followed by a master control action if required. Otherwise,normal operation may continue and a reference vector may be transmittedto all cabinets (block 530). In one embodiment, this reference vectormay be serially encoded and sent to the cabinets, e.g., via a fiberoptic interface.

Referring now to FIG. 9B, shown is a flow diagram for a basic controlloop for a cabinet in accordance with one embodiment of the presentinvention. As seen in FIG. 9B, method 550 may begin by receiving thereference vector from the master controller in a cabinet controller.From this reference vector, a switching pattern using a carried basedpulse width modulation scheme or any other modulation technique for thecells within the cabinet may be computed (block 560). In one embodiment,this PWM calculation may be in accordance with commands received fromthe master controller and general drive operation status. Then based onvarious status information, including information from ambient sensorsand the various power cells, it may be determined whether the cabinet isoperating within its operating parameters (diamond 570). If not, analarm may be triggered (block 575). Otherwise, normal operation maycontinue and the PWM signals may be sent to the power cells of thecabinet (block 580). In one embodiment, the PWM signals may be seriallyencoded and sent to the cells, e.g., via a fiber optic interface.

Referring now to FIG. 9C, shown is a flow diagram of a method forperforming control of a power cell via a local controller of the powercell in accordance with one embodiment of the present invention. Asshown in FIG. 9C, method 600 may begin by each local controllerreceiving encoded PWM signals from the cabinet controller of thecabinet. From this information gate drive signals may be computed (block610). In one embodiment, these signals may be computed by a local FPGAwithin the moveable cell section, and that these computations are basedon cell status and PWM command signals received from the cabinetcontroller. Then, based on various information including ambient sensorsand the status of the switching elements themselves, it may bedetermined whether the cell is operating within its operating parameters(diamond 620). If not, an alarm may be triggered (block 625). Otherwise,normal operation may continue and gate drive signals may be sent to theswitching elements (block 630). While shown with this particular controlimplementation in the embodiment of FIGS. 9A-9C, the scope of thepresent invention is not limited in this regard. Furthermore, understandthat the various control operations described may be performed indifferent orders and may be performed in different controllers such thatthe different control can be handled at a more local or global basisdepending on a desired implementation.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. A power cell chamber for a drive system, thepower cell chamber comprising: a moveable portion including a rectifierstage to rectify an input signal received from a secondary winding of atransformer to provide a rectified signal and an inverter stage having aplurality of switching devices to receive a DC signal and output an ACsignal, wherein the moveable portion is slidably adapted within acabinet of the drive system; and a fixed portion including a DC linkhaving at least one capacitor to receive the rectified signal andprovide the DC signal to the inverter stage, wherein the fixed portionis affixed in the cabinet, the moveable portion separate from the fixedportion.
 2. The power cell chamber of claim 1, wherein the fixed portionfurther includes an input cell protection mechanism coupled between acorresponding secondary winding and a power service bus, and a bypassblock to enable bypass of the power cell chamber.
 3. The power cellchamber of claim 1, wherein the moveable portion is formed of anenclosure having a plurality of switching devices of the inverter stageon a first side thereof and a plurality of rectification devices of therectifier stage on an opposite side to the first side, and a lowinductance path coupled between the switching devices and therectification devices, the low inductance path including at least onelocal capacitor to snub transients.
 4. The power cell chamber of claim3, wherein the moveable portion of the plurality of power cell chambersincludes a split heat sink having a first portion on which the pluralityof switching devices are adapted and a second portion on which theplurality of rectification devices are adapted.
 5. The power cellchamber of claim 1, further comprising a power service bus to couple themoveable portion and the fixed portion, and including a fixed DCconnector to mate with a corresponding DC connector of the moveableportion to couple the DC signal to the moveable portion, a plurality offixed AC connectors to mate with corresponding AC terminals to couple ACpower from a corresponding secondary winding to the moveable portion,and a plurality of fixed connectors to mate with corresponding fixedterminals of the moveable portion to enable series coupling of at leasttwo power cells.